Apparatus for testing a shear thickening plugging fluid

ABSTRACT

An apparatus for testing a shear thickening plugging fluid that is an emulsion of two components which react with each other to provide a thickening of the fluid when subjected to high stress, such apparatus comprising a cylinder (1) having an inlet (2) with an inlet valve (3) for the plugging fluid and an outlet (4) with an outlet valve (5) for the plugging fluid, a moveable piston (6) sealing against the chamber walls, so that the piston by being moved rearward in the cylinder can suck plugging fluid into the cylinder through the inlet (2), and in a retrograde movement can press the plugging fluid out through the outlet (4), a shear valve (7) connected with the outlet (4), which shear valve (7) is adjustable for adjusting a desired shear stress to be subjected upon the plugging fluid, a means (8, 9) for measuring the pressure drop over the shear valve (7), a receiver means (10) for collecting plugging fluid that has been pressed through the shear valve, and one or more means for measuring properties of the shear thickening plugging fluid.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for the testing ofdifferent properties of a shear thickening plugging fluid useful forplugging of a zone of a subterranean formation around a well bore, orfor blocking a well in case of unintended water intrusion. Theproperties of a plugging fluid that it may be of particular interest toevaluate are in particular related to setting time, shear strength andhomogeneity at different pressure and temperature conditions andchemical conditions.

2. Description of the Invention Background

For plugging of zones of subterranean formations, a use may be made i.a.of so-called "rheotropic" fluids, which fluids thicken when subjected tohigh shear. A suitable rheotropic fluid for such use is a fluid havingphysical properties enabling it to be easily pumped through the mudsystem (Condition 1) to the drill bit, and to set (Condition 2) whenforced through the nozzles of the drill bit, where the pressure dropwill be in the range of about 50 to 120 bars. Also, the time period fromthe passing through the nozzles till setting takes place must besufficiently long to enable the fluid to flow into the formation zonesto be plugged.

For the preparation of a plugging fluid having such desired settingpattern, it is known to use an emulsion technique for preparing anemulsion in which two reactive components--which will provide athickening or setting of the fluid when brought in contact with oneanother--are placed each in one separate phase of the emulsion, in sucha way that they are not brought into contact with one another. As longas the emulsion is not broken, the two reactive components will in thismanner stay separated from one another, whereby the emulsion maintainsits original low viscosity. On the other hand, when the emulsion issubjected to high shear, causing it to be broken, the two reactivecomponents will come into contact with one another and the setting ofthe fluid takes place.

Said emulsion technique can be utilized in several ways. Thus, U.S. Pat.No. 4,663,366 discloses a rheotropic water-in-oil emulsion wherein (a)the oil phase contains dispersed therein a hydratable water-swellinghydrophilic clay such as bentonite, and also contains dissolved thereina surfactant consisting of a polyamine derivative, and (b) the waterphase contains dissolved therein a polyacrylamide and a polycarboxylicacid. To keep the bentonite separated from the water until a setting ofthe fluid is desired, each droplet of the dispersed aqueous phase iscoated with a membrane or a film of a polymer material which is formedwhen the aqueous phase is dispersed or emulsified into the oil phase ofthe emulsion. The film or membrane is formed as a result of theinterfacial interaction between the polyamine derivative in the oilphase and the polyacryl amide and polycarboxylic acid in the dispersedaqueous phase. When the emulsion is subjected to high shear stress atthe desired point of time, the protective film around the disperseddroplets in the emulsion is broken and the bentonite comes into contactwith the water, which leads to a swelling of the bentonite andconsequently a thickening of the fluid.

A plugging fluid in which the emulsion technique has been utilized in adifferent manner is disclosed in Norwegian Patent Application No.931954. This plugging fluid is constituted of an emulsion comprising (a)a continuous phase containing a hydrophobic liquid (oil), an emulsifierand a cross-linking agent for a polysaccharide, and (b) a discontinuousphase containing water and a polysaccharide. In this case, the mechanismof the setting of the plugging fluid is a cross-linking of thepolysaccharide with the cross-linking agent. Thus, for achieving thedesired effect of the plugging emulsion it is critical even in this casethat the two reactive components of the emulsion are kept separated fromone another until a setting of the plugging emulsion is desired. Thisseparation is achieved by maintaining the cross-linking agentincapsulated in the hydrophobic liquid (e.g. an oil), while thepolysaccharide is incorporated in the discontinuous phase of theemulsion, which phase is an aqueous phase. Consequently, as long as theemulsion is at rest or is subjected to moderate shear stress only, nosubstantial cross-linking reaction will occur. However, when theemulsion is subjected to a high shear stress, as when squeezed through adrill bit in a borehole, the polysaccharide and the cross-linking agentwill come into contact with one another, whereby a cross-linking of thepolysaccharide takes place and the plugging emulsion sets.

The mud system employed in well and formation treatment operationsconsists of a number of units, each of which exerts shear stress to agreater or lesser extent on the fluids pumped through the system. Theshear stress is closely related to the pressure drop in each individualunit. The highest pressure drop, and thus the highest shear stress,occurs e.g. during the passage through the nozzles of a drill bit orthrough a port in a completion string down in the well. The use ofplugging fluids for the intended purpose is based on the condition thatonly flow restrictions down in the well should be capable of producing asufficiently high shear stress for the two reactive components, each ofwhich is contained in a separate phase of the emulsion, to be broughtinto contact with one another, with a resulting thickening/setting ofthe fluid.

For the plugging fluid to fulfill its purpose down in the formation, itis important (1) that it has the lowest possible viscosity in Condition1, before it is subjected to high shear stress, (2) that it thickens toa high thickness in Condition 2 after having been subjected to a highshear stress, (3) that it maintains its acquired thickness for a desiredperiod of time, and (4) that it undergoes to the least possible extent athickening in Condition 1 as a result of the emulsion graduallydeteriorating during storage or before it has been passed through thenozzles in the drill bit or other flow restrictions down in theborehole.

In order to secure that a plugging fluid fulfills its function to thelargest possible extent down in the formation, it may be desirable totest the plugging fluid before it is injected into the borehole. Inparticular, it is important to be able to recreate the shear stress towhich the plugging fluid will be exposed down in the borehole, becausethe setting time as well as the stiffness of the formed gel will dependon the shear stress to which the emulsion has been subjected.

When a liquid is flowing through a nozzle there will be a closecorrelation between the pressure drop through the nozzle and the shearstress to which the liquid is subjected in the nozzle. It wouldtherefore be possible, by using scaled down nozzle sizes, to achieve agood simulation of the conditions down in the well bore and thus predictwith a high probability how the plugging fluid will behave in practice.A testing apparatus capable of giving a realistic picture of the shearstress to which a fluid would be exposed when squeezed through e.g. thenozzles in a drill bit down in a well bore should be equipped with ameans for creating a pressure drop in the fluid of up to 120 bars,especially a pressure drop of 30 to 100 bars, and it would be practicalto carry out the testing of the plugging fluid on the basis of fluidvolumes of the order of 0.5 to 2.0 liters.

Also, an apparatus for testing rheotropic plugging fluids should bedesigned so as to prevent the fluid from being subjected to undesiredshear stress and to prevent the apparatus from being exposed toexcessive wear caused by solid particles contained in the fluid.

SUMMARY OF THE INVENTION

According to the present invention an apparatus is provided for use intesting a shear thickening plugging fluid, which apparatus fulfills saiddesires. The apparatus is characterized by the features set forth inclaim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

The apparatus and its operation is described below with reference to theappended drawings, which schematically illustrate preferred embodimentsof the apparatus.

FIG. 1 is a schematic illustration of the apparatus of the presentinvention; and

FIG. 2 is a schematic illustration of a hydraulic embodiment of theapparatus of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a cylinder 1 which is connected, via an inlet 2 at one endthereof and an inlet valve 3, with a hopper 11 for plugging fluid to betested, which plugging fluid is fed into said hopper from a mixingapparatus (not shown). At the same end the cylinder 1 has a pluggingfluid outlet 4 which is connected with an adjustable shear valve 7 viaan outlet valve 5. In front of and behind the shear valve, means 8, 9are arranged for measuring the pressure at the upstream and downstreamsides of the shear valve, respectively. A container 10 is arranged forcollecting plugging fluid from the shear valve 7. A piston 6 in cylinder1 is sealing against the cylinder wall and is moveable therein. Thus, bymoving the piston in the cylinder, plugging fluid is sucked into thecylinder through inlet 2 and in a retrograde movement of the piston theplugging fluid is pressed out through the outlet 4. The piston ispreferably driven by a hydraulic aggregate (not shown). The shear valveutilized in the apparatus can suitably be a needle valve and valves 3 to5 can suitably be ball valves.

The apparatus is operated in the following manner. The cylinder 1 isfilled with plugging fluid from the hopper 11 by the inlet valve 3 beingopened and the piston 6 being pulled into the cylinder from its endposition at inlet 2 and outlet 4, while the outlet valve 5 is maintainedin a closed position. When the piston has reached the opposite endposition and the available cylinder volume has been filled with pluggingfluid, the inlet valve 3 is shut and the outlet valve 5 is opened. Thepiston is then returned to the first-mentioned end position, whereby theplugging fluid is squeezed out of the cylinder through the outlet 4 andfurther through the outlet valve 5 and the shear valve 7 and into areceiver container 10. In the adjustable shear valve 7 the pluggingfluid is subjected to a predetermined shear stress resulting in abreaking of the emulsion and initiation of the setting process. Theshear stress is related to the pressure difference over the shear valve,i.e. to the difference between the pressures measured by pressure-gauges8, 9 in front of and behind the shear valve, respectively. By using aplugging fluid according to Norwegian Patent Application No. 931954, thesetting will occur as a result of the cross-linking agent coming intocontact with the polysaccharide and causing a cross-linking thereof.However, the setting does not occur spontaneously, however, and theplugging fluid can thus easily flow into the receiver container whereinthe setting then takes place.

In the receiver container 10, properties of the fluid such as thesetting time and stiffness (shear strength) of the formed gel aremeasured in manner known per se.

In the simplest case, the receiver container 10 is an open containerwhich is filled with the sheared plugging fluid, and the shear strengthof the gel is measured by means of standard geotechnical methods.

It may also be of interest, however, to perform the shearing of theplugging fluid against a pressure and to let the fluid set underpressure. In such a case, a pressure container is used as the receivermeans. In order to allow collection of the plugging fluid from the shearvalve, the pressure container must be equipped for withdrawal of itsinitial content under a controlled pressure. In this case, the measuringof the shear stress can be carried out either at atmospheric pressure,in which case the container is depressurized at the desired point oftime and the measurements are carried out at atmospheric pressure asmentioned above, or under an overpressure, in which case the pressurecontainer will be equipped with a high pressure consistometer equippedfor shear strength measurement.

In order to achieve measuring results giving an even better picture ofthe behaviour of the plugging fluid when being positioned in theformation zone to be plugged, it may be desirable to collect the shearedplugging fluid in a receiver container containing one or more solid,permeable materials with a selected porosity and permeability. With aknowledge of the conditions in the formation zone, one can recreate saidconditions approximately and determine with an approximate accuracy theplugging capacity of any particular plugging fluid in said zone. With areceiver container containing such solid permeable material, the shearstrength measurements can be carried out with means for measuring themaximum differential pressure which the contents of porous material andset plugging fluid in the receiver container are capable of withstandingbefore the set plugging fluid collapses.

A hydraulic embodiment of the apparatus of the invention is shownschematically in FIG. 2, where those reference numerals which also occurin FIG. 1 have the same meaning as as in FIG. 1. In this case, cylinder1 is a double-acting hydraulic cylinder which contains a drive piston(16) which is connected with, a working piston 6 via a piston rod (17).The drive piston is driven by a hydraulic aggregate comprising ahydraulic pump 15, a control valve 14 and inlet 12 and outlet 13 forhydraulic oil. The receiver means 10 and the means used for performingthe measurements may be similar to those described with reference toFIG. 1.

The apparatus according to the invention may advantageously beconstructed as a mobile unit. The piston 6 would then suitably behydraulically driven and the hydraulic pump 15 used to drive the piston6 would be arranged in a separate casing and be connected to theapparatus by means of a hydraulic quick release coupling.

EXAMPLE

The object was to predetermine the setting characteristics obtained witha given shear thickening plugging fluid when being squeezed at apressure drop of 60 bars through the nozzles of a drill bit down in awell bore.

For this purpose a test apparatus as shown schematically in the appendedFIG. 2 was used. The cylinder of the apparatus had an internal diameterof 65 mm and a neat volume of about 1.0 liter. The effective strokelength of the piston was 300 mm. The piston was driven by a hydraulicunit of trademark Hidroirma, Type UP10; P=105 bars; Q=3.0 1/min. Theshear valve was a 10 mm needle valve of trademark Nupro, Type SS-4R3A5.The piping for transport of the plugging fluid from the hopper via thecylinder and the shear valve to the receiver container was of stainlesssteel SS 316 L and had an internal diameter of 10 mm. As inlet andoutlet valves upstream and downstream of the cylinder, respectively, 10mm ball valves of trademark Whitey, Type 44-S 10 MN were used. Thereceiver container was an open container and the shear strengthmeasurements were effected with a shear strength measuring instrument ofthe trademark Sinco Torvane, Model 51602.

For use as a plugging fluid 1.375 liters of water-in-oil emulsion wereprepared in the following manner. 0.75 of water and 6.0 g of xanthanewere mixed with agitation in a 2 1 beaker (beaker 1). After 1 hour atrest 1500 g of barite were added to the mixture. In a second 2 1 beaker(beaker 2) 0.25 1 of Exxsol D60, 1.0 ml of Safemul PE (an emulsifier ontriglyceride basis) and 8.0 g of Ca(OH)₂ were mixed with agitation. Themixture in beaker 1 was then added to the mixture in beaker 2 withagitation. An emulsion having a density of 1.80 g/cm³ was obtained.

The prepared emulsion was fed to the hopper of the test apparatus, withthe piston 6 positioned in the front position and with valves 3 intosaid pressure container due to said retrograde movement of said pistonalong said cylinder and 5 closed. The shear valve 7 was adjusted to givea pressure drop of 60 bars. The inlet valve 3 was opened and the pistonwas moved hydraulically to the rear position, whereby about 1.0 1 of theemulsion was sucked into the cylinder 1. The inlet valve 3 was thenclosed and the outlet valve 5 opened, with the piston beingsimultaneously moved to the front position. This caused the emulsion tobe squeezed through the shear valve 7 via the outlet valve 5 and to becollected in the receiver container 10. The emulsion sets in 2 minutes.After 24 hours the shear strength was measured to be 14,000 Pas.

We claim:
 1. An apparatus for testing a shear thickening plugging fluid,characterized in that it comprises a cylinder having an inlet with aninlet valve for plugging fluid and an outlet with an outlet valve forplugging fluid, a moveable piston sealing against the cylinder wall, sothat the piston by being moved rearward in the cylinder can suckplugging fluid into the cylinder through the inlet, and in a retrogrademovement can press the plugging fluid out through the outlet, a shearvalve connected with the outlet, which shear valve is adjustable foradjusting a desired shear stress to be subjected upon said pluggingfluid, a means for measuring the pressure drop over the shear valve, areceiver means for collecting plugging fluid that has been pressedthrough the shear valve, and one or more means for measuring propertiesof the shear thickening plugging fluid.
 2. The apparatus according toclaim 1, characterized in that the receiver means is an open container.3. The apparatus according to claim 1, characterized in that thereceiver means is a pressure container arranged for relief of itscontent under a controlled pressure during the pressing in of theplugging fluid into said pressure container due to said retrogrademovement of said piston along said cylinder.
 4. The apparatus accordingto claim 1, characterized in that the receiver means contains one ormore solid, permeable materials having a selected porosity andpermeability.
 5. The apparatus according to claim 2, characterized inthat it comprises a means for measuring the shear strength of the setplugging fluid at atmospheric pressure according to standardgeotechnical methods, after relief of any overpressure in the receivermeans.
 6. The apparatus according to claim 3, characterized in that itcomprises a high pressure consistometer equipped for shear strengthmeasuring, for measuring of the shear strength of the set plugging fluidunder pressure.
 7. The apparatus according to claim 4, characterized inthat it comprises a means for measuring the maximum differentialpressure which the content of porous material and set plugging fluid inthe receiver means is capable of withstanding before the set pluggingfluid collapses.
 8. The apparatus according to any of claim 1,characterized in that the inlet is connected with a hopper for feedingplugging fluid from a mixing apparatus, that the shear valve is a needlevalve, and that the valves and are ball valves.
 9. The apparatusaccording to any of claim 1, characterized in that the cylinder is adouble-acting hydraulic cylinder containing a drive piston which isconnected with a working piston via a piston rod.
 10. The apparatusaccording to claim 2 characterized in that the receiver means containsone or more solid, permeable materials having a selected porosity andpermeability.
 11. The apparatus according to claim 3 characterized inthat the receiver means contains one or more solid, permeable materialshaving a selected porosity and permeability.
 12. The apparatus accordingto claim 3 characterized in that it comprises a means for measuring theshear strength of the set plugging fluid at atmospheric pressure, afterrelief of any over pressure in the receiver means.
 13. The apparatusaccording to claim 10 comprising a means for measuring the maximumdifferential pressure which the content of porous material and setplugging fluid in the receiver means is capable of withstanding beforethe set plugging fluid collapses.
 14. The apparatus according to claim11 comprising a means for measuring the maximum differential pressurewhich the content of porous material and set plugging fluid in thereceiver means is capable of withstanding before the set plugging fluidcollapses.
 15. The apparatus according to claim 2 wherein the inlet ofthe cylinder is connected with a hopper for feeding plugging fluid froma mixing apparatus, that the shear valve is a needle valve, and that theinlet and outlet valves are ball valves.
 16. The apparatus according toclaim 7 characterized in that the inlet of the cylinder is connectedwith a hopper for feeding plugging fluid from a mixing apparatus thatthe shear valve is a needle valve and that the inlet valve and outletvalve are ball valves.
 17. The apparatus according to claim 14 whereinthe inlet of the cylinder is connected with a hopper for feedingplugging fluid from a mixing apparatus, that the shear valve is a needlevalve, and that the inlet and outlet valves are ball valves.
 18. Theapparatus according to claim 8 characterized in that the cylinder is adouble-acting hydraulic cylinder containing a drive piston which isconnected with a working piston via a piston rod.
 19. The apparatusaccording to claim 2 characterized in that the cylinder is adouble-acting hydraulic cylinder containing a drive piston which isconnected with a working piston via a piston rod.
 20. The apparatusaccording to claim 17 characterized in that the cylinder is adouble-acting hydraulic cylinder containing a drive piston which isconnected with a working piston via a piston rod.